1. Field
The present invention relates to a signal transmission apparatus that transmits a signal through a transmission line and to a method of controlling the signal transmission apparatus.
2. Description of the Related Art
In recent years, Peripheral Component Interconnect (PCI) and PCI-X used in personal computers and servers are being replaced with PCI Express. Similarly, Advanced Technology Attachment (ATA) used in connection with storage devices, such as a hard disk drive (HDD) and a compact disk-read only memory (CD-ROM), is being replaced with Serial ATA and Small Computer System Interface (SCSI) is being replaced with Serial Attached SCSI.
In other words, signal transmission interfaces (electrical interfaces) are being rapidly changed from parallel interfaces to serial interfaces.
Since the serial interfaces use bandwidths wider than those of the parallel interfaces, a method is required to accurately detect any loss, jitter, noise, and/or variation on the transmission lines in order to achieve more stable transmission waveforms.
The serial interfaces each include transmission large scale integration (LSI) that transmits a signal waveform, a transmission line including a printed circuit board, a connector, and a cable, a reception LSI that receives a signal waveform, and so on.
In design of a high-speed transmission system having a transmission speed on the order of gigahertz, it is necessary to achieve an optimal transmission quality in consideration of the performances of a transmitter and a receiver, a variation in characteristics between the materials of devices and circuit boards, the characteristics of each element composing the transmission line, and noise.
A typical transmission system in related art includes a printed circuit board, a cable, and a connector, in addition to a transmission LSI and a reception LSI. Transmission and reception performances, a variation in characteristics between the materials of the LSIs, a power supply noise and a crosstalk noise, the amount of reflection, a loss in a package including printed circuit board (PCB) wires, via holes, cables, connectors, and transmission and reception LSIs, etc., should be considered in the transmission system in the related art.
An equalizer apparatus that automatically sets an equalization parameter and a pre-emphasis adjusting method for reducing the time necessary for the pre-emphasis adjustment are proposed in the related art (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2004-15622 and 2006-246191).
In general high-speed transmission, an eye opening of a received signal and an equalizer are adjusted by emphasis adjustment.
However, since a predetermined transmission clock frequency and multi-value number are used in the general high-speed transmission, the optimal transmission method is not necessarily achieved.
A transmission-reception circuit having a large number of ports is included in an LSI with an increasing number of ports used in the high-speed transmission. Accordingly, the transmission quality can possibly be degraded due to open reflection caused in open lanes and/or noises caused by concurrent operation of multiple lanes. Furthermore, it is often considered that increasing the size of an eye opening of a received signal increases the reception margin. However, reception of a waveform having a large eye opening can increase the noise inside the LSI having a large number of ports, thereby also degrading the transmission quality.